Reactions of (+)-catechin with salivary nitrite and thiocyanate under conditions simulating the gastric lumen: Production of dinitrosocatechin and its thiocyanate conjugate

Abstract

Catechins are ingested as food components and supplements. It is known that catechins are transformed to dinitrosocatechins by nitrite under acidic conditions, suggesting the possibility of their formation in the stomach because saliva contains nitrite. This paper deals with nitrite-induced transformation of (+)-catechin in methanol extracts of adzuki bean into 6,8-dinitrosocatechin in acidified saliva (pH ≈ 1.9). As the mechanism of its formation, addition of nitric oxide (NO) to (+)-catechin semiquinone radical, both of which were produced in nitrous acid/(+)-catechin systems, was proposed. The dinitrosocatechin was oxidized to the quinone by nitrous acid, and the quinone reacted with a salivary component thiocyanate producing 6′-thiocyanato-6,8-dinitrosocatechin. Since quinones are toxic, we propose a function of thiocyanate as a scavenger of the o-quinone formed from dinitrosocatechins in the stomach.

Keywords::

• adzuki bean
• nitric oxide
• quinones of dinitrosocatechins
• semiquinone radicals
• Vigna angularis

Declaration of interest

The authors report no conflicts of interest. The authors are alone responsible for the content and writing of the paper.

Part of this study was supported by Grants-in-Aid for Scientific Research (22500790 and 23500986) from the Ministry of Education and Science in Japan.